C. 4 yrs
Feedback Here , P= Rs 1000
T= 4 yrs
R= 4 %
where, P= Principal
T= Time
R= Rate
Since , Simple Interest on Rs 1000=(1000 × 4 × 4)/100= Rs 160
now, simple interest=Rs 160
P = Rs 400
R = 10 % then, T=(100 × SI)/P × R
= (100 × 160)/(400 × 10)
= 4 yr